What HTTP 505 means
RFC 9110 §15.6.6. Server rejects the protocol version. Rare with modern HTTP/1.1 and HTTP/2 universal support.
Typical causes
- Ancient HTTP/1.0 client
- Server forces HTTP/2 only
505 5xx RFC 9110 §15.6.6 HTTP Version Not Supported
Server doesn't support the HTTP version used in the request.